This invention relates to the defining of a number of data tracks on a magnetic media. In particular, this invention relates to the defining of a plurality of data tracks on a magnetic disc and the subsequent accessing of each track through the use of a servo control system.
The art of digital recording on a magnetic disc has advanced to the point where data is being recorded in ever-increasing densities on a magnetic disc surface. There are a number of approaches which can be taken in compacting the data on a magnetic disc. One approach has been to devise novel digital coding techniques which increase the information content in each magnetic recording on the disc. Another approach has been to increase the number of concentric data tracks on a disc surface to the point where the tracks are spaced extremely close to each other. This latter approach of increasing the number of data tracks must be counterbalanced by a requirement that each and every data track must be accurately accessed by a read/write transducer.
In order to closely compact the data tracks and to at the same time access each and every track, servo systems have been devised which are capable of successively positioning a read/write transducer in closely spaced increments over a magnetic disc. Each so defined position of the read/write transducer defines a data track on the magnetic disc.
One type of servo system capable of defining closely spaced positions of a read/write transducer over a disc surface employs a separate servo transducer dedicated to reading pre-recorded position information. The pre-recorded position information often exists in the form of a plurality of position information tracks on a separate disc surface. Each position information track is separately distinguishable from its immediately adjacent tracks. The read/write transducer being fixedly attached by appropriate means to the servo transducer moves with the servo transducer as it traverses the plurality of position tracks on the separate disc surface. The servo transducer and hence the read/write transducer are positioned by the servo system which is responsive to the position information sensed by the servo transducer. The servo system usually centers the servo transducer entirely over a single position information track or between two adjacent servo position tracks. In either case, at least one entire position information track is required to define a servo transducer position and hence a data track location.
An example of a pre-recorded position information system which utilizes two tracks of position information to define one data track is disclosed in commonly assigned U.S. patent application Ser. No. 430,343, filed on Jan. 2, 1974 and now U.S. Pat. No. 3,993,180, entitled "Transducer Positioning System," to Braun, et al. While the aforementioned patent application provides for an accurate delineation of data tracks, it nonetheless requires two servo tracks of information to define a data track.